X型转子发动机由于其具有体积小、比功率高、重量轻、在高转速下运行平稳等特点在增程式混合动力汽车、军用小型无人机等领域中有着非常广阔的应用前景。然而由于X型转子发动机结构的复杂性，其内部的燃烧过程一直以来都是内燃机领域研究的热点与难点之一。为了能够清晰地认识X转子发动机的缸内流场与燃烧过程，采用数值模拟的方法研究X型汽油转子发动机的当量比、预混掺氢和直喷掺氢对缸内气流运动过程、火焰传播过程和排放物生成规律的影响，为研究X转子发动机的燃烧特性提供一定的借鉴与指导。本文的具体研究内容如下：

     （1）利用CONVERGE软件构建并验证了X转子发动机的三维动态燃烧CFD模型，研究了缸内气流运动规律和火焰传播过程，并对比分析了不同当量比下的缸内燃烧过程及主要排放产物生成规律。结果表明，缸内湍流对发动机的整个工作过程有着重要作用，缸内气体在运动过程中不断有涡团的产生和耗散，使得缸内气流的紊乱程度不断变化，促进了气体的混合，有利于燃料燃烧和火焰的传播。着火之后，火焰在传播过程中，先以球面的形式向四周传播，但受缸内主流场的作用，火焰向燃烧室前侧传播的速度大于向燃烧室后侧传播的速度。当量比为1.2时，燃烧室内自由基团峰值含量最高，放热最多，缸内压力最大，平均温度最高，NO_X排放量也最多。

     （2）研究了不同掺氢体积分数下的缸内火焰传播过程和排放物生成规律，分析了不同氢气和汽油的混合比例对燃烧过程的影响。结果表明，掺氢后缸内的火焰传播速度大于未掺氢时的火焰传播速度，且掺氢体积分数越大，对火焰传播速度和放热的影响越显著，缸内压力和平均温度也越高。同时也发现掺氢体积分数越大，缸内峰值压力和峰值温度也越靠近上止点，这一现象会导致压缩负功的增加。随着掺氢体积分数的增大，中间产物的峰值也逐渐变大，瞬时放热率升高，放热量增大，这有利于燃烧过程的进行，但会使得缸内温度明显升高，导致NO_X和CO排放显著增加。

     （3）建立并验证了H₂喷射CFD模型，对比分析了不同氢气喷射位置对发动机缸内混合气形成过程、燃烧过程和排放产物形成规律的影响。结果表明，H₂射流对燃烧室内汽油和空气形成的主流场有较大影响。氢气从喷孔喷出后在主流场的作用下形成的卷吸现象会使得流向燃烧室后侧的气流分离，绕过射流区后继续向燃烧室后侧流动。在主流场的影响下，氢气在燃烧室前后两侧都有分布，但由于位置III的喷射方向与主流场方向一致，处于点火时刻时从位置III喷出的氢气在燃烧室前侧分布最多，有利于初始火核的形成。不同喷射位置下的火焰传播过程差异较大，喷射位置III的火焰传播速度最快，放热量最多，缸内峰值压力最高，缸内平均温度升高最快，同时也产生了最多的NO_X排放，而氢气喷射位置对CO的最终排放量影响较小。

     X rotary engine has a very broad application prospect in extended-range hybrid electric vehicles, military small unmanned aerial vehicles and other fields because of its small size, high specific power, light weight and stable operation at high speed. However, due to the complexity of X rotary engine structure, its internal combustion process has always been one of the hot and difficult points in the field of internal combustion engine research. In order to clearly understand the in-cylinder flow field and combustion process of X rotor engine, the effects of equivalence ratio, premixed hydrogen and direct injection hydrogen on the in-cylinder airflow movement process, flame propagation process and emission generation law of X rotor engine were studied by numerical simulation, which provided some reference and guidance for studying the combustion characteristics of X rotor engine. The specific research contents of this paper are as follows:

    (1) A three-dimensional dynamic combustion CFD model of X rotor engine was constructed and validated within CONVERGE software, and the in-cylinder gas flow motion law and flame propagation process were studied, and the in-cylinder combustion process and the main emission generation law under different equivalence ratios were comparatively analyzed. The results show that the in-cylinder turbulence plays an important role in the whole working process of the engine, and the in-cylinder gas constantly generates and dissipates vortex groups in the process of movement, which makes the degree of turbulence of in-cylinder gas flow change constantly, promotes the mixing of gases, and facilitates the combustion of fuels and the propagation of flames. After ignition, the flame in the propagation process, first in the form of a sphere to the surrounding propagation, but by the role of the main flow field in the cylinder, the flame propagation speed to the front side of the combustion chamber is greater than that to the back side. When the equivalence ratio is 1.2, the combustion chamber has the highest peak content of free radicals, the most exothermic, the highest pressure in the cylinder, the highest average temperature, and the most NO_X emissions.

     (2) The in-cylinder flame propagation process and emission generation law under different hydrogen doping volume fractions were investigated, and the effects of different mixing ratios of hydrogen and gasoline on the combustion process were analyzed. The results show that the flame propagation speed after hydrogen doping is faster than that without hydrogen doping, and the larger the volume fraction of hydrogen doping, the more significant the effects on the flame propagation speed and heat release, and the higher the pressure and the average temperature in the cylinder. It is also found that the larger the volume fraction of hydrogen doping, the closer the peak pressure and the peak temperature in the cylinder are to the upper stopping point, and this phenomenon leads to an increase in the negative work of compression. As the volume fraction of hydrogen doping increases, the peak value of the intermediate products also becomes larger, the transient heat release rate increases, and the heat release increases, which is favorable to the combustion process, but it will make the cylinder temperature increase significantly, leading to a significant NO_X and CO emissions.

     (3) The CFD model of H₂ injection was established and validated, and different hydrogen injection positions were compared and analyzed for the formation of mixture, combustion process and emission in the engine cylinder. The results show that the H₂ jet has a large influence on the main flow field formed by gasoline and air in the combustion chamber. Hydrogen is ejected from the nozzle, and then the suction phenomenon formed in the mainstream field will make the gas flow to the back side of the combustion chamber separate, and then continue to flow to the back side of the combustion chamber after bypassing the jet area. Under the influence of the mainstream field, hydrogen is distributed in the front and back of the combustion chamber, but because the injection direction of position III is consistent with the direction of the mainstream field, the hydrogen ejected from position III is most distributed in the front side of the combustion chamber at the ignition moment, which is conducive to the formation of the initial nucleus. The flame propagation process under different injection positions varies greatly, with the injection position III having the fastest flame propagation speed, the most heat release, the highest peak pressure in the cylinder, the fastest increase in the average temperature in the cylinder, and also the most NO_X emission, while the hydrogen injection position has a small effect on the final emission of CO.

[1] Gautam K. Development of fuel/engine systems—the way forward to sustainable transport[J]. Engineering, 2019, 5(03): 510-518.

[2] 李全生, 张凯. 我国能源绿色开发利用路径研究[J]. 中国工程科学, 2021, 23(01): 101-111.

[3] 中华人民共和国国家统计局. 国家年度数据[EB/OL]. (2023)[2024-03-01]. https://data.stats.gov.cn/easyquery.htm?cn=C01.

[4] 许拯瑞. “双碳目标”下传统化石能源与新能源发展趋势[J]. 石化技术, 2022, 29(09): 188-190.

[5] 毛健民. 新能源汽车发展的主要障碍与对策探寻[J]. 时代汽车, 2022, (21): 99-101.

[6] 马凯, 孔春花. 我国新能源汽车动力电池回收现状及对策[J]. 中国科技产业, 2023, 409(07): 53-55.

[7] 苏万华, 张众杰, 刘瑞林, 等. 车用内燃机技术发展趋势[J]. 中国工程科学, 2018, 20(01): 97-103.

[8] 武涛, 彭海勇, 张海波, 等. 增程式电动汽车用内燃机研究及应用综述[J]. 现代车用动力, 2022, (02): 1-6.

[9] 中商产业研究院. 2022年中国汽车及新能源汽车保有量数据统计情况[EB/OL]. (2023-01-12)[2024-03-05]. https://www.askci.com/news/chanye/20230112/0944052097941.shtml.

[10] 新华社. 图表：我国新能源汽车保有量超过2000万辆[EB/OL]. (2024-01-11)[2024-03-05]. https://www.gov.cn/zhengce/jiedu/tujie/202401/content_6925459.htm.

[11] Jewkes J, Sawers D, Stillerman R. The Wankel Rotary piston engine [M]. The Sources of Invention. London; Palgrave Macmillan UK. 1969.

[12] 丁彦辞, 郭朋彦. 转子发动机技术国内外现状与趋势[J]. 汽车实用技术, 2017, (16): 6-9.

[13] Meng H, Ji C, Wang S, et al. A review: Centurial progress and development of Wankel rotary engine[J]. Fuel, 2023, 335: 127043.

[14] Cihan O, Kutlar O A. Effect of leading and trailing spark plugs on combustion, fuel consumption and exhaust emission in a Wankel Engine[J]. Arabian Journal for Science and Engineering, 2021, 46(8): 7471-7482.

[15] Picard M, Tian T, Nishino T. Predicting gas leakage in the rotary engine—part I: apex and corner seals[J]. Journal of Engineering for Gas Turbines Power, 2016, 138(06): 1-8.

[16] Eberle M K, Klomp E D. An evaluation of the potential performance gain from leakage reduction in rotary engines[J]. SAE Transactions, 1973, 82(01): 454-460.

[17] Picard M, Tian T, Nishino T. Predicting gas leakage in the rotary engine—part II: side seals and summary[J]. Journal of Engineering for Gas Turbines Power, 2016, 138(06): 1-8.

[18] Picard M, Tian T, Nishino T. Modeling of the rotary engine apex seal lubrication [R]. SAE Technical Paper, 2015.

[19] Shkolnik A, Shkolnik N. Cycloid rotor engine[P]. US0294747A1, 2012.

[20] 吴进军, 王西峰, 梁健光. 多种燃料转子发动机技术及其发展[C]. 中国动力工程学会成立四十周年文集, 转子发动机专业委员会, 2002: 6.

[21] Shkolnik A, Shkolnik N, Scarcella J, et al. Compact, lightweight, high efficiency rotary engine for generator, apu, and range-extended electric vehicles[C]. Proceeding of the NDIA Ground Vehicule Systems Engineering and Technology Symposium, Novi, Michigan, USA, 2018.

[22] 王志辉, 孙忠刚, 简忠武, 等. 汪克尔转子发动机的研究进展及应用现状[J]. 设备管理与维修, 2019, 460(22): 60-62.

[23] 李辉, 孙非. 转子发动机应用发展与关键技术[J]. 小型内燃机与车辆技术, 2023, 52(03): 68-74.

[24] 杨道荫, 梁健光, 白效介, 等. 多种燃料转子发动机现状与前瞻[J]. 机电产品开发与创新, 2001, (03): 13-16.

[25] 李长道. 四冲程气口式三缸两弧转子发动机[P]. 中国专利: CN2821179, 2006.

[26] 计敏涛, 赵新年. 耐磨损环保低耗能“8”字形转子发动机及其转子以及做功方法[P]. 中国专利: CN108757167, 2018.

[27] 冯莉莉, 冯泽航, 王伟. 一种汽油转子发动机[P]. 中国专利: CN112302787A, 2021.

[28] 纪常伟, 史梦圆, 汪硕峰. 一种用于转子发动机的密封系统[P]. 中国专利: CN113898494A, 2022.

[29] 耿琪, 王学德, 杜洋, 等. 点火时机对X型转子发动机燃烧性能的影响[J]. 空军工程大学学报, 2022, 23(06): 17-24.

[30] Yang Z, Du Y, Geng Q, et al. Performance analysis of a hydrogen-doped High-Efficiency Hybrid Cycle rotary engine in high-altitude environments based on a single-zone model[J]. Energies, 2022, 15(21): 7948.

[31] 耿琪, 王学德, 杨正浩, 等. 不同供氢方式对X型转子发动机性能影响的仿真研究[J]. 西安交通大学学报, 2023, 57(02): 78-89.

[32] Geng Q, Wang X D, Du Y, et al. Effect of the hydrogen injection position on the combustion process of a direct injection X-Type Rotary Engine with a hydrogen blend[J]. Energies, 2022, 15(19): 7219.

[33] 张泽奇, 杜洋, 杨正浩, 等. 不同氢气喷孔直径对汽油掺氢X型转子发动机性能及污染物排放影响[J]. 西安交通大学学报, 2024, 58(02): 66-78.

[34] Hou Y, Du Y, Gao X, et al. Comprehensive comparison of single-stage and novel two-stage hydrogen direct injection strategies on the combustion and thermodynamic performance of X-type rotary engine using gasoline-hydrogen fuel[J]. International Journal of Hydrogen Energy, 2024, 53: 441-456.

[35] Shkolnik A, Littera D, Nickerson M, et al. Development of a small rotary SI/CI combustion engine[C]. SAE Technical Paper Series, 2014.

[36] Littera D, Nickerson M, Kopache A, et al. Development of the XMv3 high efficiency cycloidal engine[C]. SAE Technical Paper, 2015.

[37] Shkolnik N, Nickerson M, Littera D, et al. Progress in development of a small rotary SI engine[C]. 2015.

[38] Costa T J, Nickerson M, Littera D, et al. Measurement and prediction of heat transfer losses on the XMv3 rotary engine[J]. SAE International Journal of Engines, 2016, 9(4): 2368-2380.

[39] Leboeuf M, Dufault J-F, Nickerson M, et al. Performance of a low-blowby sealing system for a high efficiency rotary engine[C]. SAE Technical Paper Series, 2018.

[40] Nickerson M, Kopache A, Shkolnik A, et al. Preliminary development of a 30 kW heavy fueled compression ignition rotary ‘X’ engine with target 45% brake thermal efficiency[C]. SAE Technical Paper Series, 2018.

[41] Lee C, Yu H, Kimdohyun, et al. Validation of CFD analysis and flow characteristics of GP3 rotary engine at motoring condition[J]. Journal of The Korean Society of Combustion, 2020, 25(3): 11-20.

[42] Lee C, Kimdohyun, Yu H, et al. Validation of CFD analysis and combustion characteristics of GP3 rotary engine at firing condition[J]. Journal of The Korean Society of Combustion, 2020, 25(3): 21-30.

[43] 何盛宝, 李庆勋, 王奕然, 等. 世界氢能产业与技术发展现状及趋势分析[J]. 石油科技论坛, 2020, 39(03): 17-24.

[44] 国务院. 关于印发《2030年前碳达峰行动方案》的通知[EB/OL]. (2021-10-26)[2023-07-13]. https://www.gov.cn/zhengce/content/2021-10/26/content_5644984.htm.

[45] 国家发展改革委. 国家发展改革委、国家能源局联合印发《氢能产业发展中长期规划(2021-2035年)》[EB/OL]. (2022-03-23)[2023-05-25]. http://www.nea.gov.cn/2022-03/23/c_1310525755.htm.

[46] Verhelst S, Wallner T. Hydrogen-fueled internal combustion engines[J]. Progress in Energy and Combustion Science, 2009, 35(6): 490-527.

[47] Meng H, Ji C, Xin G, et al. Comparison of combustion, emission and abnormal combustion of hydrogen-fueled Wankel rotary engine and reciprocating piston engine[J]. Fuel, 2022, 318: 123675.

[48] Dincer I, Acar C. Review and evaluation of hydrogen production methods for better sustainability[J]. International Journal of Hydrogen Energy, 2015, 40(34): 11094-11111.

[49] Leu J H, Lan T S, Su A, et al. Effect of different fuels (methane, methanol, and hydrogen) on rotary engine operation[J]. Sensors and Materials, 2021, 33(1): 479-484.

[50] 李径定, 陆英清, 杜天申, 等. 汽油-氢混合燃料燃烧的试验研究[J]. 内燃机工程, 1982, (04): 52-58.

[51] Duan X, Liu Y, Liu J, et al. Experimental and numerical investigation of the effects of low-pressure, high-pressure and internal EGR configurations on the performance, combustion and emission characteristics in a hydrogen-enriched heavy-duty lean-burn natural gas SI engine[J]. Energy Conversion and Management, 2019, 195: 1319-1333.

[52] Garcia-Agreda A, Di Sarli V, Di Benedetto A. Bifurcation analysis of the effect of hydrogen addition on the dynamic behavior of lean premixed pre-vaporized ethanol combustion[J]. International Journal of Hydrogen Energy, 2012, 37(8): 6922-6932.

[53] Salzano E, Cammarota F, Di Benedetto A, et al. Explosion behavior of hydrogen–methane/air mixtures[J]. Journal of Loss Prevention in the Process Industries, 2012, 25(3): 443-447.

[54] Wang D, Ji C, Wang S, et al. Numerical study of the premixed ammonia-hydrogen combustion under engine-relevant conditions[J]. International Journal of Hydrogen Energy, 2021, 46(2): 2667-2683.

[55] Gao J, Xing S, Tian G, et al. Numerical simulation on the combustion and NOx emission characteristics of a turbocharged opposed rotary piston engine fuelled with hydrogen under wide open throttle conditions[J]. Fuel, 2021, 285: 119210.

[56] Dhyani V, Subramanian K A. Control of backfire and NOx emission reduction in a hydrogen fueled multi-cylinder spark ignition engine using cooled EGR and water injection strategies[J]. International Journal of Hydrogen Energy, 2019, 44(12): 6287-6298.

[57] Gao J, Wang X, Song P, et al. Review of the backfire occurrences and control strategies for port hydrogen injection internal combustion engines[J]. Fuel, 2022, 307: 121553.

[58] Wang H, Ji C, Su T, et al. Comparison and implementation of machine learning models for predicting the combustion phases of hydrogen-enriched Wankel rotary engines[J]. Fuel, 2022, 310: 122317.

[59] Meng H, Ji C, Su T, et al. Analyzing characteristics of knock in a hydrogen-fueled Wankel rotary engine[J]. Energy, 2022, 250: 123828.

[60] Su T, Ji C, Wang S, et al. Idle performance of a hydrogen rotary engine at different excess air ratios[J]. International Journal of Hydrogen Energy, 2018, 43(4): 2443-2451.

[61] Zambalov S D, Yakovlev I A, Maznoy A S. Effect of multiple fuel injection strategies on mixture formation and combustion in a hydrogen-fueled rotary range extender for battery electric vehicles[J]. Energy Conversion and Management, 2020, 220: 113097.

[62] Chen W, Yu S, Zuo Q, et al. Combined effect of air intake method and hydrogen injection timing on airflow movement and mixture formation in a hydrogen direct injection rotary engine[J]. International Journal of Hydrogen Energy, 2022, 47(25): 12739-12758.

[63] Meng H, Ji C, Yang J, et al. Experimental study of the effects of excess air ratio on combustion and emission characteristics of the hydrogen-fueled rotary engine[J]. International Journal of Hydrogen Energy, 2021, 46(63): 32261-32272.

[64] Amrouche F, Erickson P, Park J, et al. An experimental investigation of hydrogen-enriched gasoline in a Wankel rotary engine[J]. International Journal of Hydrogen Energy, 2014, 39(16): 8525-8534.

[65] Su T, Ji C, Wang S, et al. Idle performance of a hydrogen/gasoline rotary engine at lean condition[J]. International Journal of Hydrogen Energy, 2017, 42(17): 12696-12705.

[66] Su T, Ji C, Wang S, et al. Improving the combustion performance of a gasoline rotary engine by hydrogen enrichment at various conditions[J]. International Journal of Hydrogen Energy, 2018, 43(3): 1902-1908.

[67] Itkis E, Fedyanov E, Levin Y. Experimental and numerical investigation of influence of hydrogen addition to hydrocarbon fuel on wankel rotary engine performance[C]. Proceedings of the 4th International Conference on Industrial Engineering, 2019: 2079-2087.

[68] Shi C, Chai S, Di L, et al. Combined experimental-numerical analysis of hydrogen as a combustion enhancer applied to wankel engine[J]. Energy, 2023, 263: 125896.

[69] Yang J, Ji C, Wang S, et al. Numerical investigation on the mixture formation and combustion processes of a gasoline rotary engine with direct injected hydrogen enrichment[J]. Applied Energy, 2018, 224: 34-41.

[70] 范宝伟, 潘剑锋, 肖曼. 不同氢气喷射方式对天然气掺氢转子发动机燃烧过程的影响[C]. 中国内燃机学会燃烧节能净化分会2015年学术年会论文集, 2015: 221-228.

[71] 廖忠权. 液体活塞公司开发的重油转子发动机[J]. 航空动力, 2018, (05): 33-34.

[72] 卢法, 余乃彪. 三角转子发动机[M]. 北京: 国防工业出版社, 1990.

[73] 陆尧. 航空煤油转子发动机的喷雾及燃烧特性研究[D]. 江苏大学, 2020.

[74] Fan B, Pan J, Tang A, et al. Experimental and numerical investigation of the fluid flow in a side-ported rotary engine[J]. Energy Conversion and Management, 2015, 95: 385-397.

[75] Abraham J, Bracco F V. Comparisons of computed and measured mean velocity and turbulence intensity in a motored rotary engine[J]. SAE Transactions, 1988, 97: 1701-1713.

[76] Han Z, Reitz R D. Turbulence modeling of Internal combustion engines using RNG k-ε models[J]. Combustion Science and Technology, 1995, 106(4-6): 267-295.

[77] 郭尚群, 赵坚行. RNG k-ε模型数值模拟油雾燃烧流场[J]. 航空动力学报, 2005, (05): 807-812.

[78] Senecal P, Pomraning E, Richards K, et al. Multi-dimensional modeling of direct-injection diesel spray liquid length and flame lift-off length using CFD and parallel detailed chemistry[J]. SAE Transactions, 2003, 112(3): 1331-1351.

[79] Spreitzer J, Zahradnik F, Geringer B. Implementation of a rotary engine (Wankel Engine) in a CFD simulation tool with special emphasis on combustion and flow phenomena[C]. SAE Technical Paper, 2015.

[80] Turns S R. Introduction to combustion[M]. New York, NY, USA: McGraw-Hill Companies, 1996.

[81] Ranzi E. A wide-range kinetic modeling study of oxidation and combustion of transportation fuels and surrogate mixtures[J]. Energy & Fuels, 2006, 20(3): 1024-1032.

[82] Pitz W J, Cernansky N P, Dryer F L, et al. Development of an experimental database and chemical kinetic models for surrogate gasoline fuels[J]. SAE Transactions, 2007, 116(3): 195-216.

[83] Liu Y D, Jia M, Xie M Z, et al. Enhancement on a skeletal kinetic model for primary reference fuel oxidation by using a semidecoupling methodology[J]. Energy & Fuels, 2012, 26(12): 7069-7083.

[84] Pan S, Wang J, Huang Z. Effects of hydrogen injection strategy on the hydrogen mixture distribution and combustion of a gasoline/hydrogen SI engine under lean burn condition[J]. International Journal of Hydrogen Energy, 2022, 47(57): 24069-24079.

[85] Zschutschke A, Neumann J, Linse D, et al. A systematic study on the applicability and limits of detailed chemistry based NOx models for simulations of the entire engine operating map of spark-ignition engines[J]. Applied Thermal Engineering, 2016, 98: 910-923.

[86] Zeldvich Y B. The oxidation of nitrogen in combustion and explosions[J]. J Acta Physicochimica, 1946, 21: 577.

[87] Yang J, Ji C, Wang S, et al. A comparative study of mixture formation and combustion processes in a gasoline Wankel rotary engine with hydrogen port and direct injection enrichment[J]. Energy Conversion and Management, 2018, 168: 21-31.

[88] 李向荣, 付经伦, 马维忍. 内燃机内流动的研究[J]. 车用发动机, 2003, (01): 1-5.

[89] 陈秋亮. 缸内直喷式柴油/天然气双燃料转子发动机的数值模拟研究[D]. 中南大学, 2008.

[90] 夏一帆, 赵冬梅, 葛海文, 等. 环形燃烧室点火过程的实验与数值研究[J]. 浙江大学学报(工学版), 2020, 54(02): 416-424.

[91] 何磊, 龚岩, 郭庆华, 等. 甲烷/氧气层流同轴射流扩散火焰OH*自由基的数值研究[J]. 光谱学与光谱分析, 2018, 38(03): 685-691.

[92] Smirnov N, Nikitin V. Modeling and simulation of hydrogen combustion in engines[J]. International Journal of Hydrogen Energy, 2014, 39(2): 1122-1136.

[93] Yang J, Ji C. A comparative study on performance of the rotary engine fueled hydrogen/ gasoline and hydrogen/n-butanol[J]. International Journal of Hydrogen Energy, 2018, 43(50): 22669-22675.

[94] 夏基胜. 低热值燃气-柴油双燃料发动机动力性能计算[J]. 小型内燃机与摩托车, 2010, 39(6): 48-51.

[95] Wang T, Zhang X, Zhang J, et al. Numerical analysis of the influence of the fuel injection timing and ignition position in a direct-injection natural gas engine[J]. Energy Conversion and Management, 2017, 149: 748-759.

[96] Yang B, Wei X, Xi C, et al. Experimental study of the effects of natural gas injection timing on the combustion performance and emissions of a turbocharged common rail dual-fuel engine[J]. Energy Conversion and Management, 2014, 87: 297-304.

[97] Mansor M R A, Nakao S, Nakagami K, et al. Ignition characteristics of hydrogen jets in an argon-oxygen atmosphere [R]. SAE Technical Paper, 2012.